18 ALASKAN GLACIER STUDIES Unalaska was visited by Theodore Blake in 1867,1 under the direction of Davidson.4 When visited by Jagger in 1907 it showed no signs of retreat, nor did the glaciers on the island of Atka.8 In 1889 Russell4 visited Unalaska and concluded that there had been no general glaciation of the Aleutian Islands, although local glaciers had existed. CENTRAL PLATEAU AND BEBINQ SEA Yukon and KusleoTcwim Valleys. The lack of former glaciation in the Central Plateau of Alaska was established by Dall,B Dawson,6 McConnell,7 Russell,8 Hayes,9 Spun-,10 Tyrrell,11 Brooks,13 and others. Detailed topographic maps and geological investigations have failed to show existing glaciers within most of this great area, but that they were formerly present east of the Klondike district and in the upper Lewes, Teslin, Pelly and Macmillan Rivers is abundantly proved. In the region between the Tanana and Yukon Rivers the prospectors "Annual glaciers" referred to by Spurr,18 Barnard14 and Prindle1B seem to be only long-lived snowbanks that melt before the summer is over. One region where these are abundant is called Glacier Mountain. Streams in the interior of Alaska which freeze solid and then overflow and freeze again are also known locally as "glaciers." The photographs from the Yukon-Tanana region show cirque-like amphitheatres at the heads of many streams and it seems likely that local glaciers formerly existed. This part of the Central Plateau rises to heights of 8000 to 6000 feet but has an annual precipitation of only 12 inches. In part of the region between the Yukon and Koyukuk Rivers Mendenhail has shown1B conclusively that there has been no glaciation but in another area between these rivers EaMn17 found evidence of local glaciation in 1918. In the Kuskokwim Mountains which rise to 4500 feet above sea level, there were formerly local glaciers, in a small area recently described by Maddren,18 who finds cirques, moraines, and other conclusive evidence. i House Extra Doc. 177, 40th Congress, 2d Session, 1868, p. 323. a Davidson, George, Trans, and Proc. Geog. Soc., Pacific, Vol. HI, 1904, pp. 9-11; Appalachia, Vol. IV, 1884. • Journ. GeoL, Vol. XVI, 1908, p. 668. «Bull. GeoL Soc. Amer., Vol. I, 1890, pp. 138-180. « Doll, W. H., Amer. Journ. Sci., VoL XLV, 1868, p. 99. • Dawson, G. M., GeoL and Nat. Hist. Survey Canada, Ann. Kept., VoL TTT, Part 1,1889, p. 164B. • McConnell, R. G., Bull. GeoL Soc, Amer., Vol. I, 1890, pp. 548-644. • Russell, I. C., Surface Geology of Alaska, Bull. Geol. Soc. Amer., Vol. I, 1890, pp. 140-141. «Hayes, C. W., Nat Geog. Mag., Vol. IV, 1892, pp. 155-159 and Pis. 19 and 20. « Spurr, J. E., 18th Ann. Kept., U. S. Geol. Survey, Part m, 1897, p. 270. "• Tyrrell, J. B., Bull. Geol. Soc. Amer., VoL X, 1899, pp. 195-198. n Brooks, A. H., 20th Ann. Kept., U. S. Geol. Survey, Part Vn, 1900, p. 474; 21st Ann. Kept., U. S. Geol. Survey, Part n, 1901, pp. 864-366; Maps and Routes of Exploration in Alaska in 1898, Special Publication, U. S. Geol. Survey, 1900, pp. 69, 91. » Spurr, J. E., 18th Ann. Rept., U. S. Geol. Survey, Part HI, 1898, pp. 820-823. K Barnard, E. C., Maps and Descriptions of Routes of Exploration in Alaska in 1898, Special Publication, U. S. Geol. Survey, 1899, p. 79. " Prindle, L. M., Bull. 875, U. S. Geol. Survey, 1909, p. 12. n MendenhalL W. C., Professional Paper 10, U. S. GeoL Survey, 1902, pp. 45-^6. n Eakin, H. M,, personal communication. " Maddren, A. G., The Innoko Gold-Placer District, Alaska, Bull. 410, U. S. Geol. Survey, 1910, pp. 18-15, 58-60.